The formal semantic web, now linked data, using RDF is largely flailing in most regions outside the UK. The main problem is the complexity in implementation compared with the tools typically used by web sites, for example, PHP, CSV, MySQL. However, a large part of the world uses Javascript for their development. JSON-LD has emerged as a proposal to tie back end systems together with a widely reusable JSON intermediary based on RDF structure. Are there any significant sites or project that use JSON-LD?

Gmail, Search Answer Cards, and Google Now rely on structured data in emails to work. Schemas in Gmail supports both JSON-LD and Microdata and you can use either of them to markup information in email. This lets Google understand the fields and provide the user with relevant search results, actions, and cards. For example, if the email is about an event reservation, you might want to annotate the start time, venue, number of tickets, and all other information that defines the reservation.

Yep, we're looking at JSON-LD within HTML emails as a way to better expose and notify people about information within municipal meeting agendas and public notices. We'll send you an email alert with that Google can pick up and show you in email and importantly Google Now.
– drikiMay 17 '13 at 17:32

I really don't know what your beef is with this technology, or what it is you think you are critiquing, but it's clear you have something in your head that you think defines a technology. The use of various linked data approaches has been accepted by such "small" companies as Google, Facebook, Microsoft and Yahoo, and is becoming a mainstay of a number of projects including, but not limited to, Open Data. If there's a specific criticism that is motivating your question, then I'd suggest doing some homework, understanding what it is you are asking, and being more precise.